Electrical resistance and art of forming the same



Dec. 10, 1929. H. FENDER ETAL ELECTRICAL RESISTANCE AND ART OF FORMING THE SAME Filed Aug. 22, 1924 INVENTORS Wm J. mm

' ATTORNEY.

Patented Dec. 10, 1929 UNITED STATES PATENT oFncE ELECTRICAL RESISTANCE AND ART OF FORMING THE SAME Application filed August 22, 1824. Serial No. 733,478.

This invention relates to electrical resistance media and devices and methods of production thereof.

One of the objects of the invention is to rovide a practical resistor characterized y certain desirable features in use. An-

other object is to provide an electrical resistance medium of reliable and efiicient action and simple construction. Another ob- 1 ject is to provide a construction of the above nature which shall be inexpensive in manufacture and adapted for a ready variation of effective'resistance; Another object is to provide an art of producing devices and media, such as the above, which can be conveniently carried on with dependable results.

Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, and in the steps and combinations of steps, all as will be illustrativel hereinafter described, and the scope of t e application of which will be indicated in the following claims.

In the accompanying drawing, in which are shown two of various possible embodiments of the mechanical features of this invention,

Fig. 1 is a central, longitudinal sectional view of a variable resistor;

Fig. 2 is an end view of a certain part shown in Fig. 1;

Fig. 3 is an end view of another part shown in Fig. 1; and

Fig. 4 is a central, longitudinal sectional view of a non-variable resistor.

Similar reference characters refer to similar parts throughout the views shown'in the drawing.

Referring now to Figs. 1, 2 and 3, there is shown at 10 a piece of tubing formed of glass or other suitable insulating material and having on its inner walls, as at 11, a coatin or film of a high resistance.

his coating 11 is preferably formed of metallic germanium, which may be deposited on the glass in the form of an extremely w thin film, and possesses certain highly desirable characteristics for use in this relation.

One method of producing this film or mirror is as follows: Pure granulated aluminum and a small amount of distilled water are placed in a suitable receptacle, and caustic soda added to liberate hydro en so as to completely fill the container. small amount of germanic acid is then admitted to the container and the nascent hydrogen reacts with the germanic acid, forming germanic hydridea colorless gas. This gas mixed with hydrogen is permitted to pass through the tube 10, the latter being atthat time heated to such temperature that its walls verge on softening. This heated surface causes the germanic hydride to decompose andfdeposit a mirror of pure germanium on the walls. By regulating the inflow of germanic acid, and thereby the amount of germanium hydride, transmitted through the tube, the rate of formation of the mirror may readily be controlled, and may, of course, be stopped at any desired thickness of the film. Also, by a suitable gradation of temperature of the glass from end to end, or by a slow feeding of the germanic hydride through the tube, the film may be caused to vary in thickness so as to taper from a maximum thickness, as at 12, to a minimum thickness at the other end, as at 13. Such a tapering of the thickness of the film presents certain advantages in the use of this invention, although the broader features are not limited to a coating of unequal depth.

To the ends of the tube 10 are attached r metal caps 1 and 2. Ca 1 is preferably attached to the tube by p acing in the ca a suitable quantity of a metallic alloy fusible at a low temperature and a small quantity of powdered rosin. The cap is then heated until the allo and rosin melt, whereupon the end of the tube is pressed into the cap, which is then allowed to cool. The alloy is then found to take the form shown at 3, making metallic contact between the cap 1 and the coating 11. A sufiicient quantity of rosin rises between the cap 1 and the outside of the tube 10, as shown at 4, to hold the cap securely to the tube. Cap 2 is secured to the other end of the tube 10 by sealing wax or other suitable cement.

.The inner end 15 of this sprin The resistor is connected to the electric circuit of which it is to form a part by placing it between spring contacts 17 and 18 of the form commonly used in wireless receiving ap aratus.

assing through a central opening 20 in the terminal member 2 is a plunger rod 21 having at its outer end a suitable finger rest 22 made of rubber or other insulating material. This finger rest is made of such a diameter that it may be passed readily through the opening 19 in the clip 18. The plunger 21 is intended to make connection with the terminal member 2 and shunt a variable portion of the resistance afforded by the film 11. It is preferably provided at its inner end with alight spiral spring 14 made of fine wire. is rigidly attached to the plunger so that t ere can be no relative motion of this end of the spring 14 and the plunger 21. The outer portion 16 of this sprin rests against the germanium coating 11 an makes electrical connection with this coating and the plunger 21. The germanium coatlng 11 adheres so firmly to the glass tube 10 that the rubbing of the spring 14 over this coating does not wear it off, so that the'plunger 21 may be pushed back and forth repeatedly without impairing the effectiveness of the device.

To insure positive electrical contact between the plunger 21 and the terminal member 2 a specially-shaped spring 5 is placed inside this member before the latter is attached to the tube 10. This spring is made of fine spring wire and is so shaped that when the plunger 21 is inserted in the terminal member 2, the inner portion 6 of this spring presses firmly against the plunger and the outer portion 7 presses firmly against the inner wall 8 of the terminal member 2.

In the use of the device shown in Fig.

1, it is inserted between the pairs of clips 17 and 18 in a suitable circuit, such as the socalled grid leak circuit of wireless receiving apparatus. The film is of such thickness as to give an electrical resistance of the desired order, and by a suitable movement of the plun er 22 this resistance may be adjusted to the esired value. Due to the character of the various parts, the resistance once set is maintained at precisely the desired value, and the noises sometimes caused by the grid leaks in wireless reception are obviated. Furthermore, by the tapering of the thickness of the film to give a constantly decreasing electrical resistance per unit of length toward the thicker end of the film, any given longitudinal displacement of the plunger will give the same percentage variation of the remaining resistance. This is of value in many relations.

It will also be seen that the apparatus is unafi'ected by use or by variations in surrounding temperature, it being understood that the spring 14 is of an extremely light construction, just sufiicient to make a satisfactory electrical contact.

One form of non-variable resistor embodying certain features of this invention is shown in Fig. 4. A fine rod or fiber 24 of glass or other suitable insulating material is first given a coating 25 of germanium by placing this fiber inside a tube which is heated to such temperature that this fiber verges on softening, and gassing a mixture of germanium h dride an hydrogen throu h this tube in t manner previously descri ed. This rod or fiber 24 is then mounted'inside a suitable protecting tube 23 which latter is provided with metal caps 26 attached thereto by rosin or other suitable cement 28. Electrical contact between the germanium coating 25 and the caps is made by a suitable low-melting point alloy 27. The procedure in mounting the rod or fiber inside the tube 23 is as follows:

One of the caps 26, into which has been placed the requisite amount of low-melting point alloy and rosin, is heated until the alloy and rosin melt, whereupon the tube 23 is inserted into the cap and immediately thereafter the fiber is inserted into the tube 23 and its end pressed into the molten alloy and held there until the cap has cooled. The alloy in cooling contracts around the fiber, holds it securely and makes electrical connection between the germanium coating thereon and the cap 26. The other cap 26, into which has been placed the requisite amount of low-melting point alloy and rosin, is then heated until the alloy and rosin melt, and the other end of the tube 23 containing the fiber 24 is inserted therein and the cap allowed to cool. This form of construction is particularly well adapted to the roduction of resistors having a resistance 0 1 or more megohms per inch of length, for by using a fiber of suitably small diameter the cross section of the germanium film deposited thereon may be made as small as desired, and yet of suflicient thickness to insure permanence.

It will thus be seen that there is provided apparatus and an art in which the several objects of this invention are achieved and which are well adapted to meet the conditions of hard practical use.

As Various changes might be made in the illustrative construction herein described, and as the art herein set forth might be varied, all without departing from the scope of the invention, it is understood that all matter herein set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. The herein described art of forming an electrical resistance which comprises heating a non-conducting tube and passing germanium hydride therethrough.

of that herein described, in combination, a

vitreous member havin formed thereon a film of germanium, an means adapted to lead current through said film. fT

5. In a construction of the general nature of that herein described, in combination, a glass tube, a film of germanium formed on the inner surface of said tube, means adapted to make connection with said film adjacent one end of said tube, a member slida'bly mounted within said tube and making a sliding connection with said film, and means adapted to leadcurrent to said movable memher.

6. In a construction of the general nature of that herein described, in combination, a glass tube, a film of germanium formed on the inner surface of said tube, means adapted to make connection with said film adjacent one end of said tube, a member slidably mounted within said tube and making a sliding connection with said film, and means adapted to lead current to said movable member, said film being of increasing thickness in the direction toward said first connecting member.

7. The herein described art of forming an electrical resistance which comprises heating a glass member to a temperature'approximating that at which it softens and passing germanium hydride over the surface thereof.

8. In a device of the class described, in combination, a-glass tube, means within said tube forming an electrical conductingpath of high resistance, a metal cap into which the end portion of said tube projects, a fusible metallic alloy within said cap and forming an electrical connection between said cap and said conducting means within said tube, and a film of rosin between the inner wall of said cap and the outer wall of said tube for securing said cap and said'tube together.

9. In a device of the class described, in combination, a tube made of insulating material, a film of conducting material extending through said tube substantially from one end to the other, a metal cap enclosing an end of said tube in electrical contact with said film, a cap secured to the other end of said tube and insulated from said film, a conducting member slidably mounted in said second cap for moving longitudinally of said tube, spring means for making electrical connection between said member and said film, and spring means for making electrical connection between saidmember and said second cap.

10. In a device of the class described, in combination, a tube made of insulating material, a film of conducting material extending through said tube substantially from one end to the other, a metal cap enclosing an end of said tube in electrical contact with said film, a cap secured to the other end of said tube and insulated from said film, a conducting member slidably mounted in said second cap for moving longitudinally of said tube, a spring having electrical connection with said member and adapted'to make substantially circumferential contact with said film at points spaced from said first cap, and means for insuring electrical connection between said member and said second cap.

11. In a device of the class described, in combination, a tube made of insulating material, a film of conducting material extending through said tube substantially from one end to the other, a metal cap enclosing an end of said tube in electrical contact with said film, a cap secured to the other end of said tube and insulated from said film, a conducting member slidably mounted in said second cap for moving longitudinally of said tube, a spring having electrical connection with said member and adapted to make substantially circumferential contact with said film at points spaced from said first cap, and a second spring having an electrical contact with said member and adapted to make substantially circumferential contact with the inner wall of said second cap.

12. The herein described art of forming an electrical resistance which comprises depositing a metallic film upon the inner walls of a tubular member, heating a metal ca containing a mixture of rosin with a fusib e metallic alloy to a temperature sufficient to melt said rosin and said alloy, and then thrusting an end of said tubular member into said melted mixture to establish metallic electrical connection between said film and said cap and an adhesive layer of rosin between said cap and the outer wall of said tubular member.

In testimony whereof, we have signed our names to this specification this 12th day of Aug., 1924.

- HAROLD PENDER.

JOHN H. MUELLER. 

